Pneumatic tire having multiple modulus body cord to reduce rolling resistance

ABSTRACT

A pneumatic tire includes a body having a plurality of main body cords. The tire includes an upper section above the maximum section width and a lower section below the maximum section width. The modulus of the body cords is configured to be larger in the lower section than in the upper section. This modulus ratio decreases the rolling resistance of the tire. The increased modulus in the lower section is achieved by providing intermediate body cords disposed between the main body cords. In another embodiment, the increased modulus is achieved by changing the material and/or size of the cords in the lower section.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional application of U.S. patentapplication Ser. No. 09/492,205 filed Jan. 27, 2000; the disclosures ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention generally relates to pneumatic tires and,more particularly, to a pneumatic tire having a multiple modulus bodycord that improves the rolling resistance of the tire. Specifically, thepresent invention is directed to a pneumatic tire having a body corddivided into upper and lower sections wherein the ratio of the modulusof the upper section to the modulus of the lower section is reduced inorder to decrease the rolling resistance of the tire. The ratio isreduced by providing additional body cords in the lower section or byincreasing the modulus of the cords in the lower section.

[0004] 2. Background Information

[0005] In an inflated and loaded condition, a radial tire is subject tobending moments at the shoulder areas in both the leading and trailingpositions of the tire footprint. The strains and stresses created by themoments are directly related to the rolling resistance of the tire.Previous research and studies have focused on reducing the density ofstrain caused by the bending moments to reduce rolling resistance. Onetheory to reduce rolling resistance in a pneumatic tire is to increasethe eccentricity (ECY) of the tire. Eccentricity is the ratio of belttension (BT) over body cord tension (BCT). ECY thus equals BT/BCT. Ingeneral, a higher ECY will result in lower rolling resistance.

[0006] The art has also determined that ECY is related with fundamentalstiffness and primarily with radial stiffness (K_(r)). Fundamentalstiffness is a group of three parameters measured through a speciallydesigned testing machine. The three parameters are lateral stiffness(K_(s)), radial stiffness (K_(r)), and tangential stiffness (K_(t)). Theeccentric stiffness (E_(cc)) may be defined as πr(K_(r)+K_(t)). ECY isinversely proportional to E_(cc). A tire with a lower K_(r) will thushave a higher ECY and lower rolling resistance.

[0007] In the past, rolling resistance requirements have been met bychanging the materials or design parameters of the tire. Most tiredesigns change the tread compound in order to meet the rollingresistance requirements. Changing the tread compound is generallyundesirable and the art desires another method for reducing the rollingresistance in tire design.

BRIEF SUMMARY OF THE INVENTION

[0008] In view of the foregoing, an aspect of the present invention isto reduce the rolling resistance of a pneumatic tire by improving thecarcass design. In particular, the invention improves the rollingresistance by optimizing the body cord stiffness. The inventionoptimizes body cord stiffness by dividing the body cord in a tiresection into three sections and optimizing the ratio of stiffnesses ofthe areas to reduce rolling resistance.

[0009] The invention provides a relationship between the body cordtension ratio and the radial stiffness and a relation between radialstiffness and the rolling resistance of the tire.

[0010] The invention also provides a pneumatic tire having a multiplemodulus body cord tire by applying the concepts of the invention toreduce rolling resistance. The invention is thus achieved by a pneumatictire including a body having maximum section width. The tire alsoincludes an upper section above the maximum section width and a lowersection below the maximum section width. The tire further includes a plyof body cords disposed in the body. The modulus of the body cord ply inthe lower section is larger than the modulus of the body cord ply in theupper section.

[0011] The invention also provides a pneumatic tire including a bodyhaving maximum section width with an upper section above the maximumsection width and a lower section below the maximum section width. Thetire also includes a plurality of body cords disposed in the body. Eachof the body cords having an upper section and a lower section whereinthe lower section has a larger modulus than the upper section.

[0012] The invention further provides a pneumatic tire including a bodyhaving maximum section width with an upper section above the maximumsection width and a lower section below the maximum section width. Aplurality of body cords are disposed in the body. An intermediate cordis disposed between each pair of body cords in the lower section of thebody.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0013] The preferred embodiment of the invention, illustrative of thebest mode in which applicant contemplated applying the principles of theinvention, is set forth in the following description and is shown in thedrawings and is particularly and distinctly pointed out and set forth inthe appended claims.

[0014]FIG. 1 is a cross sectional view of a pneumatic tire having theimproved multiple modulus body cord;

[0015]FIG. 2 is an enlarged fragmentary view of the tire of FIG. 1 withthe multiple modulus body cord;

[0016]FIG. 3 is an enlarged fragmentary view with portions broken awayand in section looking in the direction of arrows 3-3, showing thepreferred embodiment for changing the modulus of the body cord in theturn up portion of the tire;

[0017]FIG. 4 is a sectional view taken along line 4-4 of FIG. 3;

[0018]FIG. 5 is a sectional view taken along line 5-5 of FIG. 3;

[0019]FIG. 6 is a view similar to FIG. 3 showing an alternativeembodiment of the invention;

[0020]FIG. 7 is a sectional view taken along line 7-7 of FIG. 6; and

[0021]FIG. 8 is a view similar to FIG. 3 showing a second alternativeembodiment of the invention.

[0022] Similar numbers refer to similar elements throughout thespecification.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The tire having reduced rolling resistance is indicated generallyby the numeral 10 in the accompanying drawings. Tire 10 includes a ply12 of body cords 14 that are disposed in a body cord plane 16 (see FIG.4). Tire 10 also includes a pair of bead rings 18 disposed at the lowerends 20 of tire 10. Ply 12 extends inside each bead ring 18, wrapsaround the bottom of each bead ring 18, and then turns up outside beadring 18 to double back on itself. Tire 10 may also include a single or aplurality of belt plies 22. Each of the plies 12 and 22 is disposed inthe body 24 of tire 10.

[0024] The body cord tension, fundamental stiffness., and rollingresistance of tire 10 are first determined by any of a variety ofmethods known in the art with a finite element analysis being thepreferred method. The invention applies the body cord tension ration(BCTR) concept to design a low energy loss radial tire. The followingparameters are first determined to design tire 10:

BCTR _(bead) =BCT _(bead) / BCT _(total)

BCTR _(shldr) =BCT _(shldr) /BCT _(total)

[0025] BCTR_(bead) is the body cord tension ratio in the bead section34. BCTR_(shldr) is the body cord tension ratio in the shoulder area 32.BCT_(bead) is calculated from the maximum section width 28 to the end ofturn up when tire 10 is inflated. When multiple body cords 14 arepresent, multiple body cord tensions in this area are summed.BCT_(shldr) is the summation of body cord tension from the edge of thefirst belt to maximum section width 28 in an inflated condition. Whenmultiple body cords 14 are present, multiple body cord tension in thisarea are summed. BCT_(total) is the summation of body cord tension fromthe center of the tire section to the end of turn up in an inflatedcondition. Again, when multiple body cords 14 are present, multiple bodycord tension in this area are summed.

[0026] In accordance with one of the features of the present invention,BCTR_(bead) is closely related with K_(r) and a tire with higherBCTR_(bead) had a lower K_(r) value. As discussed above, a lower K_(r)will reduce rolling resistance. In order to calculate BCTRbead, tire 10is divided into a tread section 30, shoulder section, 32, and beadsection 34. BCT_(shldr), BCT_(bead), and BCT_(total) are then calculatedto obtain BCTR_(bead).

[0027] In accordance with the features of the present invention, tire 10includes a multiple modulus body cord 14. The modulus referred to inthis application is the modulus of elasticity for cords 14. Ply 12 ofbody cords 14 is first divided into an upper section 40 (disposed abovemaximum section width 28 from point C to A in FIG. 2) and a lowersection 42 (disposed below maximum section width 28 from point C to E inFIG. 2). Lower section modulus (M_(lower)) is the modulus of body cord14 in lower section 42. Upper section modulus (M_(upper)) is the modulusof body cord 14 in upper section 40.

[0028] In one example, tires with M_(lower) indexes of 60, 80, 100, and120 and M_(upper)/M_(lower) at 0.75, 1, 1.33 were reviewed. This reviewshows that the smaller M_(upper)/M_(lower) ratio has a higherBCTR_(bead) and lower rolling resistance. For instance, if tire 10 hasM_(upper)/M_(lower)=0.75 and M_(lower) indexed at 80, tire 10 has 7%less radial stiffness, a 4% higher BCTR_(bead) value, and 2% lessrolling resistance than a control tire having M_(upper)/M_(lower)=1.0.

[0029] The preferred embodiment of tire 10 thus includes an intermediatebody cord 50 disposed between each body cord 14 in lower section 42 asdepicted in FIG. 3. Intermediate body cords 50 increase the M_(lower)and thus decreases the rolling resistance of tire 10. In the preferredembodiment of the invention, intermediate body cords 50 are disposed inthe same body cord plane 16 as body cords 14 as depicted in FIG. 5.Cords 50 are spaced from and substantially parallel to cords 14. Analternative embodiment of the invention is depicted in FIGS. 6 and 7. Inthe embodiment of tire 10 depicted in FIGS. 6 and 7, intermediate bodycords 50 are offset from body cord plane 16 by an offset 52. Cords 50are also parallel to cords 14 in the alternative embodiment depicted inFIGS. 6 and 7.

[0030] A second alternative embodiment of the multiple modulus tire isindicated generally by the numeral 100 in FIG. 8. In this embodiment,tire 100 includes main body cords 102 having upper sections 104 andlower sections 106. Lower section 106 have a higher M_(lower) in orderto decrease the rolling resistance of tire 100. Upper section 104 isconnected to lower section 106 by a connector 108. The modulus in lowersection 106 is increased by fabricating lower section 106 from adifferent material than upper section 104. The lower section 106 mayalso be formed to have a different cross sectional area or shape thanupper section 104.

[0031] The invention is not limited to the specific illustrative detailsthat appear above. Other variations and modifications are equivalent forthe stated and illustrated functions without departing from the spiritor scope of the invention as defined by the following claims.

[0032] Accordingly, the improved tire with multiple modulus body cord toreduce rolling resistance apparatus is simplified, provides aneffective, safe, inexpensive, and efficient device which achieves allthe enumerated objectives, provides for eliminating difficultiesencountered with prior devices, and solves problems and obtains newresults in the art.

[0033] In the foregoing description, certain terms have been used forbrevity, clearness, and understanding; but no unnecessary limitationsare to be implied therefrom beyond the requirement of the prior art,because such terms are used for descriptive purposes and are intended tobe broadly construed.

[0034] Moreover, the description and illustration of the invention is byway of example, and the scope of the invention is not limited to theexact details shown or described.

[0035] Having now described the features, discoveries, and principles ofthe invention, the manner in which the tire with multiple modulus bodycord to reduce rolling resistance is constructed and used, thecharacteristics of the construction, and the advantageous new and usefulresults obtained; the new and useful structures, devices, elements,arrangements, parts, and combinations are set forth in the appendedclaims.

1. A pneumatic tire, comprising: a body having maximum section width, anupper section above the maximum section width, and a lower section belowthe maximum section width; a plurality of body cords disposed in thebody; each of the body cords having an upper section disposed in theupper section of the body and a lower section disposed in the lowersection of the body; and the lower section of each body cord having alarger modulus than the upper section of the body cord.
 2. The tire ofclaim 1, further comprising a connector connecting each body cord uppersection to a body cord lower section.
 3. The tire of claim 2, whereinthe body cords are spaced apart and substantially parallel.
 4. The tireof claim 1, wherein the upper section of each body cord is fabricatedfrom a different material than the body cord lower section.
 5. The tireof claim 1, wherein the body cords in the upper section have a differentdiameter than the body cords in the lower section.
 6. A pneumatic tire,comprising: a body having maximum section width, an upper section abovethe maximum section width, and a lower section below the maximum sectionwidth; a ply of body cords disposed in the body; the ply of body cordsdisposed in both of the upper and lower sections of the body; the ply ofbody cords including a plurality of main body cords; each of the mainbody cords having a lower section disposed in the lower section of thebody and an upper section disposed in the upper section of the body; aplurality of the body cords having a lower section with a larger modulusthan the upper section; and the modulus of the body cord ply in thelower section being larger than the modulus of the body cord ply in theupper section.
 7. The tire of claim 6, wherein each body cord havingdifferent modulus including a connector connecting the body cord uppersection to the body cord lower section.
 8. The tire of claim 7, whereinthe body cords are spaced apart and substantially parallel.
 9. The tireof claim 6, wherein each body cord having different modulus has theupper section of each body cord fabricated from a different materialthan the body cord lower section.
 10. The tire of claim 6, wherein eachbody cord having different modulus including the body cords in the uppersection have a different diameter than the body cords in the lowersection.
 11. A pneumatic tire, comprising: a body having maximum sectionwidth, an upper section above the maximum section width, and a lowersection below the maximum section width; a ply of body cords disposed inthe body; the modulus of the body cord ply in the lower section beinglarger than the modulus of the body cord ply in the upper section; andthe ply of body cords including a plurality of main body cords; aplurality of the main body cords including first and second cordsportions; the first cord portion being disposed in the upper section;the second portion being disposed in the lower section; the modulus ofthe second portion being higher than the modulus of the first portion.12. The tire of claim 11, wherein each of the main body cords includesfirst and second cords portions; the first cord portion being disposedin the upper section; the second portion being disposed in the lowersection; the modulus of the second portion being higher than the modulusof the first portion.